Three-phase welding system with postheat control



June 17, 1952 SOLOMON 2,600,585

THREE-PifASE WELDING SYSTEM WITH POSTHEAT CONTROL Filed Feb. 9, 1950 4 Sheets-Sheet l 75 n m 5' -24 J3 Z8 72 June 17, 1952 J. soLoMoN THREE-PHASE WELDING SYSTEM WITH POSTHEAT CONTROL Filed-Feb. 9, 1950 fiznsvajor JZZAZ'LZJL figfawov. W 444 Q/W M June 17, 1952 J. L. SOLOMON 2,600,585

Filed Feb. 9, 1950 g ikz/erzjaz' Ljfiwj Jo/amoza.

Patented June 17, 1952 THREE-PHASE -WELDIN G SYSTEM WITH P OSTHEAT CONTROL J S c lo oil; 'C liicagmIlL, assignor to. Weldchi'lncl, Chicago,' IlL, a corporation Aifiiiiaiioli statin 1956, serial Nd. 143, 241 Moraine. (01. 323 -34) 1 The invention relates to candor c'i'rc ts and has refer'frcelin parti r toan' improved'1elec5 troni'c control and timing circuit es p pial ly designed for em n g'japparatus for producing single or multiple welding" pulses o'f lvaria'blei duration depending: on the heat control also roducing such'vlz eldlngpulse s controlled uecja'y 'of' h ghljeldingcurrent for postheating' the weldnietal to anneal the same.

. Thef Sc'iakYPatent 24314183 granted Noivmbeijieg ro ig di sc s l translat "'g' sy'st" in for transferring ehergyf' iroi n a o y hasea te tmg cu rent. source tiil ll a circuit suchasafweliiinggc fi and w g a y one of three'types of powermajbe'secured inthe welding circuit such as a sing1 nid1reuona1 current impulse a series o'f'uhldirectional current ni q 'th a n f ol r orias es'qi current m u ses; 'a h nim e being" QPPQSi in. polarity to the one'imrnediafie y preceding itand so comprising} form of single phase alternatin e t: Mb eg ar l l n he t fislpha ethree-windingsystem of said patent employsreac'tanc'c' means-in the form ofpri n'ar'y windings in inductive relation with" a secondary load circuit and wherein each primary winding has individual' circuit connections to its respective phase of the polyph'ase source ofosupply with electric discharge devices of the ignit'ron'type being provided -for 'controllingthe rectified currents supplied to the "windings respectively An'object of the present invention is to provide improved, simplified and eflilcien't control circuit for 'firing the ele'ctric'di's'charge devices in a welding system' as described and wherein said discharge devices' comprise 'two'group's and which are rendered conductive in an alternate manner to pass current to the primary windings for predetermined welding periods with controllable periods of'ofitime between eachwelding period.

Another object ,of the invention is to provide anelectronic control and timing "circuit for a in s wh ch. c b ,manu lly senior producing a single welding pulse o f controlled a n. .0? for P du in m l l We n Pulses. d w h n e m n s t or pr d ci sueh pulses of a modulated wave shape comprising a weldingpulsefollowed by a controlled decay of the welding current for postheating the weld r A 'furtherobject of the invention resides in the provision 'of anl 'electronicpontrol circuit for the purposes ec s-raped, which .will incorporate f proved' mansr r has sh nin me cqr tro gnd voltages for firing the electriadlsc'harge devices with respect a the wagesappearmgaertsg the polyphase source ofsupply whereby to controlthe magnitude of the current delivered to the "res'pective windings for each energizing impulse.

Another object isto provide a novel phase.

shifting circuit having phase shifting nifeahs for" controlling l the magnitude of 7th" rent 'land als'o having phase shif v V i controlling themagnitudeof the postheat'ing' cur rent. .l A, A Still m e. bie

reversing circuits especially designed for control- 1 l ng the firing'fof the'ighi'tron'tubs in, afweld ng.

system and whiclrfwillincorporate sepaifate a d.

independent phase shiftingmeansfor'contr the magnitud'e .of the welding? current ahd thje,

postheating'current respectively, and whereinthev control circuit arrangement when manually .set will operate automatically at theend of tli we ing period toishi'ft from thewelding 'ph means to the postheating phasesh ift means. .t

A further object of the invention is to piovi'de a fully electronic reversing and timingcircui't rgr I rendering'groups'of ignitrons alternately conductive and nonconductive and wherein thesaid re} versing and timing circuit will incorporate a pair' of electric valves alsoloperatingin an alternately conductive manner to provide said reversing control, with the switch from one valvelto the other being automatic by reasonof the circuit elements.

.With these and various'oth er objects in view, the invention mayfl consist of certain novelfeatures'of construction and operation as will be more fully described and particularly pointed Figure .2 is a schemata etail. intimate? the, adjustable phase shifting circuit .0; the 1111-. ventlon and which controls the magnitude of the welding current and also the postheating current;v

.E ii

ranger nents therefore as incorporated in" the condest-w ry means for 3 trol and timing circuit of the present invention;

Figure 4 is a schematic wiring diagram showing another part of the control circuit of Figure 3 and which incorporates an electronic valve for effecting the automatic switching from one phase shift means to the other for postheating;

Figure 5 is a portion of the control circuit shown in Figure 3 enlarged, the same illustrating the reversing electric valves which control the potentials applied to the grids of the ignitrons;

Figure 6 is a portion of the control circuit of Figure 3 enlarged, the same showing the circuit connections for the adjustable resistance controlling the off time;

Figure '7 is a portion of the control circuit of Figure 3 enlarged, the same showing the circuit connections for the adjustable resistance controlling the on time; and

Figures 8 to 11 show reproductions of actual oscillograms of welding current pulses comprising the output of a system embodying the improvements of the present invention.

Referring more particularly to Figure 1, the invention is illustrated as applied to a three phase welding system which is characterized by an in- 1 ductive device such as a welding transformer having a plurality of primary windings in inductive relation with a secondary winding, it being understood that the welding load circuit includes the secondary winding since the welding current is induced therein. No disclosure has been made of the secondary winding since the same is conventional, and'only the primary circuit of the welding transformer has been disclosed as having three primary windings which are individually connected to a phase of the three phase source of supply. The leads L1, L2 and L3 represent the conductors of the three phase alternating current supply source and which are so connected to the welding transformer Iii that primary winding II is connected across L1 and L2, with primary winding |2 being connected across L2 and L3, and primary winding l3 being connected across L3 and L1. Each primary winding may comprise a number of windings connected in series but for illustrative purposes each primary winding has been shown as including a pair of windings with the ignitron tubes being located therebetween. For example, primary winding includes windings M and I5 and which have electrical connection with a pair of ignitron tubes l6 and I1 disposed between the windings and which tubes are connected in anti-parallel, or, in other words, the cathode of one is electrically connected to the anode of the other. Primary winding l2 includes windings l8 and IS) with ignitron tubes 20 and 2| being connected between the windings in anti-parallel relation with each other. Primary winding l3 includes windings 22 and 23, the same having ignitron tubes 24 and 25 electrically connected in antiparallel relation and disposed between the windings. In operation of the system as disclosed the ignitrons for the various primary windings perform a controlling function so that positive or negative half cycles of alternating current are supplied to the windings in sequence according to the phase relation of the electromotive forces in the three phase supply line. For example, the ignitrons I6, 20 and 24, constituting one group, are rendered conductive for passing positive half cycles of current in sequence according to the phase relation of the electromotive forces in the polyphase supply. Before the magnetizing effect of tromotive forces.

the flow of one positive half cycle through winding dies out the phase relation of the electromotive forces in the three phase supply is such that the next half cycle of positive current is supplied to winding l2 and thereafter to winding |3 and the same continues in sequence for the duration of the welding period. Since the magnetizing current impulses flow in the same direction through the primary windings the magnetic flux will continue to rise until a predetermined maximum is reached, when the ignitrons are simultaneously rendered non-conductive. This rise in the magnetic flux has the effect of inducing a unidirectional current in the secondary circuit (not shown) and which constitutes a single welding impulse. See Figure 8. For the next operation of the system as disclosed the ignitrons l1, 2| and 25, comprising the second group, are rendered conductive and negative half cycles of current are passed through the respective windings according to the phase relation of the elec- However, the current flow in each primary winding is now opposite in direction to the positive half cycles although they have the same effect of producing a unidirectional rise in the magnetic flux to induce a unidirectional current in the secondary circuit. The polarity of this unidirectional current is opposite to the welding impulse produced by the positive half cycles and so a form of alternating current can be secured from the present system by rendering the groups of ignitrons alternately conductive. See Figure 9.

The reversing control and timing circuit of the invention is designed to render the groups of ignitrons alternately conductive and to control the magnetizing period, that is, the weld time, and also control the o time between successive welding impulses. This is accomplished through the provision of common cathode and grid points, respectively, the same having connection with the grid-cathode circuits of thyratrons or firing valves which are provided to control the conductivity of the ignitrons. By applying control potentials to common cathode and grid points it is possible to render the groups of ignitrons conductive in an alternate manner and to conveniently regulate the length of the conducting period and the length of the off time between said periods. For a complete description of a three phase welding system such as disclosed, having common cathode and grid points providing a sequence control circuit for the ignitrons thereof, reference is made to my copending application Serial No. 34,538, filed June 22, 1948, and entitled Sequence Control Circuit and Timer.

The thyratrons for the ignitrons l6 and I! are indicated by numerals 26 and 21, each thyratron consisting of an anode, a cathode, and having a control grid and a screen grid. The screen grid 28 for thyratron 26 is connected to the secondary winding 29 of transformer 30. The control grid 3| for said thyratron 2B is electrically connected to the secondary winding 32 of transformer 33, the said secondary having electrical connection through conductor 34 to common grid point B for the group of ignitrons, namely, I6, 20 and 24. Thyratron 21 has its screen grid 35 connected to secondary winding 36 of transformer 30, whereas, its control grid 31 is connected to secondary winding 38 of transformer 40, the said winding having connection to the common grid point C for the second group of ignitrons, namely, 2| and 25.

ace-asst in a similar manner ignitronsand 2| are provided with thyratrons or firing valves 4! and 42 and the same structure is provided for ignitrons 24 and 25 which have the thyratrons Hand 55 associated therewith. The circuit for each thyratron is the same as described for '26 and 21, it being understood that the control grids and screen grids have electrical connection with secondary windings of the transformers as indicated for purposes which will be presently described. It may be mentioned that the primaries of the transformers '30, and 58.- are located in the phase shift control of Figure 2.

Thyratrons 26, 4| and 54 will control the firing of the first group of ignitrons and will maintain them conductive for a predetermined period of time. depending on the control of the thyratrons. In a similar manner thyratrons- 21, 42

and 55 will control the second group or ignitron'sand will also maintain them conductive for apredetermined period of time depending on the control of the thyratrons. In operation of the present welding system all the tubes are held in a quiescent state by maintaining the grid points B and C highly negative with respect to the commo'n cathode point A, Figure 2. When it is desired to render the first group of ignitron tubes conductive point B is made slightly positive with respect to point A and C is maintained negative as before. Ignitron tubes [6, 20 and 24 are accordingly fired and are maintained conductive for a period of time which is preset b'y'the' timing control to be presently described. At the end of the'weld time point B is made negative with respect to point A as before and after a predetera mined 0001" time point C is made slightly positive. The ignitron tubes ll, 2| and 25 are now fired and they remain conductive for the preset interval as determined by the adjustment ofthe timing control.

In order to provide a common cathode point a plurality oftransformers connect point A with the leads L1, L2 and L3, respectively, all as clearly shown in Figure 2. Conductor connects point A with the terminal point 66 of lead L1 and this conductor includes the primary winding 61 of the transformer 40 having the two secondary windings 38 and 60. Conductor 68 connects point A with terminal point 69 of lead L2 and the conductor includes a primary winding 10 of the transformer 33. In a similar manner conductor H connectspoint A with the terminal point12 of lead L3, the conductor including a primary winding 13 of the transformer 48. It'isnec'essary that high impedance means be included in each conductor otherwise the primary windings H, I2 and I3 would be short circuited. l-his accounts for the windings 6'1, 1'0 and 13 of the transformers 40, 33 and 48, each of which has two secondary windings, the same being located-in the grid cir-- cuits forthe thyratrons respectively. Since current is flowing through conductors- 65, 68- and H at all times the current flow through windings 61, I0 and 13- will produce an alternating-current voltage across each winding. It is necessary to cancel out said alternating current voltages if the desired control voltages are to be impressed between the grid and cathode terminals of the firing valves. The alternating current. voltages appearing across each of the windings in the conductors for point A are cancelled out by the equal and opposite voltage induced in the secondary windings provided therefor respectively. The

firing valves will thus have impressed between.

he a id-andcathodeterminalsthereoi.whatever control voltages are applied to the point A and B and'A'andG.

During the conducting periods for the groups of ignitron's another condition exists in that a direct current voltage appears across each wind-- ing of the welding transformer primaries H, [2 and -3. This will be understood byobserving Figures 1 and 2 which clearlyshows each pri mary winding as connected in series relation with the cathode circuit of its respective firing valve. For reasons explainedit is necessary-to cancel this direct current voltage developed across each primarywinding due to flow of current in the same and which is effected by a transformer 15; having a p imary winding T6 and two seccanary-windings 11 and 18. The primarywind ing 16 is connected across windin 2-3, for example, or the welding transformer and secondary winding H is connected with the gridpoint B andwith a voltage source tobe presentlydescribed which applies the control potentials to grid point B. Ina similar manner econdarywinding 18 is connected by conductor 8|" with grid point C- and with said voltage source which applies the control potentials tosaid gridpoint C. The voltage induced in each secondary is equal and opposite to the direct current voltageac'ross} aprimary winding of" the welding transformer andeach secondary is electrically conin-series relation with" the grid circuit of one group of-=flr-in'g valves. Without this transformer structure the" following action would 're-' sult. One groupof ign'itrcnsupon bein condu'ctiv'e would pass current through the windings of the welding transformer. As new of cur rent continues the voltage developed" across the windings;ofthe welding transformer; and w-hichare connected to the cathode of the thyratrons,

would bring thei'r g'rids' negative with respect tothecathodes and this would render the ignitronnonconducting. The secondary windings Tl andwere introduced in the respective grid circuits and in this waythey'c'ancel the undesired voltages; and the ignitronsare completely responsiveto-th'e control'voltagesapplied to pointsB and-C. It was previously explained that thethyratrons Would-fire to render the ignitrons-conductive upon the application of a positive potential to p'ointsB or C with respect to the common cathode point A. The control voltages appliedto'- thegrid pointsB and C are effective-to fire the thy-ratrons provided the screen grids-of thesociatedwithprimary windings 8 2 provided by the phase shift device of Figure 2. In a similar manner-the. secondary-- windings 44 and SI of transformer- 45 are" inductively" associated with the: primary windings -83 and the secondarie -5 l and 62 of transformer 58 are inductively-associated with'the primary winding 84. By shifting thezvoltage across the respective primary windings 82'; 83 :and- 84 :with respect to the line. voltage' of thesrespective phases it is .possible to hold:

the screen grids ofthethyratrons in-aneg'ative condition for a period act-time. after the control:

gridsrarerender'ed positive. following the start'of a;-;.positive..-or-negative-half: cycleas regards \thee The secondary windings. 2S

to control the magnitude ofthe welding impulse and in accordance with the invention the phase shift arrangement of Figure 2 includes phase shift means for controlling the magnitude of the welding current and separate and independent phase shifting means operating automatically at the end of the weldingperiod for controlling the postheating current.

The phase shift device of Figure 2 essentally consists of conductors 85, 86 and 81 connected in delta relation to the three phase supply line, it being observed that conductor 85 is connected across phase Ll-LZ and that the same has in series therewith the fixed resistor 88 and an adjustable resistor 90, the latter having a slider 9|. Conductor 86 is connected across phase L2L3 and has connected in series therewith resistor 92 and the adjustable resistor 93 having the slider 94. In a similar manner conductor 81 is connccted across phase Ila-L1, and the same i connected in series with the resistor 95 and the adjustable resistor 99 having the slider 91. The pri-' mary windings 82, 83 and 84 are connected to the adjustable resistors through their sliders by means of relay actuated contactors I00, each contactor I having a current limiting resistor II'II in parallel therewith and it will be observed that the contactors I90 are normally closed so that a connection through the sliders with the phase shifting circuit consisting of the adjustable resistors 90, 93 and 96 and the fixed resistors 88, 92 and 95. As a result of the normally closed contactors I00 the primary windings 82, 83 and 84 are normally connected across the respective phases of the power supply line by said phase shifting circuit and accordingly the same constitutes the. device for controlling the magnitude of the weldin current. In operation of the present welding system the firing of the thyratrons can be delayed for a fraction of a half cycle, depending on the setting of sliders 9|, 94 and 91, which are mechanically joined so that they can be rotated in synchronism and to a like extent. By the adjustment of sliders 9|, 94, 91, for example, the current flowing through winding 82 instead of being in phase with L2-L3, the phase of said current is shifted toward L1L2. Also with respect to the current flowing through winding 83 by adjustment of sliders 9|, 94 and 91, the phase is shifted toward L2La, and in a similar manner the phase of the current flowing through winding 84 is shifted by adjustment of sliders 9|, 94, 91 toward L3-L1. As previously explained, the winding 82 constitutes the primary of the transformer having the two secondaries 29 and 36 so that when a positive voltage is applied to their screen grids after a predetermined delay, the respective thyratrons are caused to fire to render the ignitrons I9 and I1 conductive. The phase shift with respect to primary winding 83 and primary winding 84 is similar to that described so that the transformer and 58 and their respective secondary windings are controlled in a similar manner and firing of their thyratrons is also delayed so that all the ignitrons are rendered conductive at the same relative point in the half cycles.

When the sliders 9|, 94 and 9'! are set as described the welding current will be somethin is normally maintained less than the maximum for the particular weld-' ing device. When the sliders are rotated in the direction of the arrows to the maximum extent, the welding current will be at the maximum since in this position the voltage across the primary winding 82 will have been advanced so that it becomes more nearly in phase with LlL2 and the voltage across the primary winding 83 will be advanced toward L2Ls and likewise the voltage across primary winding 84 will be advanced toward Ila-L1. The positive potentials applied to the screen grids of the thyratrons will be substantially in phase with their respective line voltages so that the thyratrons will fire at the start of the half cycles and maximum current will be passed through the primary windings of the welding transformer.

It will be further understood that when sliders 9|, 94 and 91 are rotated to secure the minimum heating eifect, the setting of the sliders will be such as to shift the voltages so that the voltage across winding 82 will be substantially in phase with L2Lc, and to shift the voltage across winding 83 so that'the same will be substantially in phase with LaL1, and likewise with respect to winding 84, the voltage will be shifted so that the same is substantially in phase with L1L2. This setting will produce a phase shift of degrees and represents the minimum heat setting for the present welding system.

In accordance with the invention the phase shift device of Figure 2 includes-a separate and independent phase shifting circuit for controlling the magnitude of the postheating current, the same being automatically rendered operative at the end of the welding period, provided the present system is manually set for postheating. Conductor I02, connected across phase L1--L2 includes the fixed resistor I03 and the adjustable resistor I64 having the slider I95. Conductor I96 connected across phase L2-l s includes the fixed resistor Ill! and the adjustable resistor I08 having the slider I09. The conductor IIO connected across phase Ila-L1 includes the fixed resistor III and the adjustable resistor ||2 having the slider H3. The sliders I05, I99 and H3 are mechanically connected together so that they may be simultaneously rotated and to a like extent. The phase shifting circuit just described is electrically connected to the windings 82, 83 and 84 through the sliders I65, I99 and H3 by means of the relay-actuated contactors II4. A current limiting resistor H5 is connected across each contactor H4 and it will be seen that the said contactors are normally open so that the phase shifting device for controlling the postheating current is inoperative except when the contactors I|4 are closed. The operation of the relay-actuated contactors I69 and H4 is such that the two sets of contactors are energized simultaneously so that one set, namely, contactors I00, are caused to open when the other set, namely, contactors II4, are caused to close. The effect of this operation is to render the phase shifting circuit for controlling the welding current inoperative and to render operative the phase shifting circuit for controlling the postheating current. Since postheating is eifected by a controlled decay of the current in the welding circuit it necessarily follows that the setting of the sliders I85, I09 and H3 is such as to produce a considerably lower current than is produced by the setting of the sliders 9|, 94 and 91.

The common cathode point A is connected by a conductor III! to the resistance II9 by means of the slider I20, Figure 3. Said resistance II9 constitutes a voltage divider so that the potential on the common cathode point A can be regulated by'moving the slider I along the resistance. The power supply for said resistance H9, which constitutes a source of direct current for the operation of the timing circuits, consists of transformer I2I having connected thereto the full wave rectifier tube I22 for supplying direct current to the respective terminals of the resistance H9. The usual reactor I23 and the condenser I24 are included in the circuit, all in accordance with conventional practice.

The vacuum tube I25, Figures 3 and 6, having through slider I33 with the negative end of resistance H3. The adjustable resistor I34 is connected across the terminals of condenser I30, the said resistor providing adjustment for varying the off" time, sometimes referred to as the "0001 time, between welding impulses. charging condenser I an independent power source is provided including transformer I35 and rectifying device I36, the same having suitably connected across its terminals condenser I31 and the resistance I38. The negative end of this power source is connected through conductor I to the peaking transformer I4I, which in turn has suitable connection with the control grid I28 of tube I21. The switch I42 is normally closed and in order to start an on time period the switch must be opened to allow condenser I30 to. discharge through adjustable resistor I34. The negative bias normally applied to grid I28 of tube I21 is gradually made more positive until presently a pulse from the peaking transformer I4I will fire tube I21, causing the same to conduct and establish the circuit also including tube I25 and the diode I3I. When tube I21 is conducting the potential applied to one of the grid points, either B or C, in the welding transformer is made positive with respect to the common cathode point A so that one group of ignitrons is rendered conductive to induce a welding current impulse in the secondary circuit by how For time condenser I41 will discharge through tube I46 since a pulse from peaking transformer I50 will render its control grid I5I positive. The numerals I 52, I53 and I54 comprise control switches and it will be assumed for purposes of this description that the slider for each switch is located at position No. 1, which position renders the postheating elements of the control circuit inoperative. The slider for each switch may also be located in a No. 2 position which renders the postheating elements of the control circuit operative. As a result a gradual and com trolled decay of the welding current takes place as will be hereinafter described in detail. For position No. 1 the control circuit will produce a single welding impulse or a plurality of welding impulses, depending on the length of time switch I42 is held open, and it will of course be under;- stood that switch I42 may be actuated manually or the switch may be included in an automatic arrangement for predetermining the welding pulses delivered by the present system. For a single welding pulse it is only necessary to momentarily open switch I42 since a firing of tube I21 will initiate the welding operation and the same will continue until the cycle has beencompleted even though switch I42 may have been previously closed. With the sliders of switches I52, I53 and I54 in No. 1 position tube I46wlll discharge through windings I55 and I56 of transformers I51 and I58, respectively, having secondary windings I64 and I61. The discharge of current through winding I55 of transformer, I51 is such as to deliver a negative pulse to grid I26 of tube I 25 to thereby stop conduction through said tube and its associated circuit including the control tube I21 and diode I3I. This accord ingly terminates the on time period. Referring again to the pulse through winding I55,- it will be understood that the sliders of switches I59, I60, I6I, I62 and I63 are all in position No. 1 so that the secondary winding I64 is thus con nected at one end through conductor I65 to the grid I26 andat its opposite end through conductor I66 to the cathode of said tube I25.

The discharge of condenser I41 through tube I46 and through winding I56 of transformer I58 will energize its secondary winding I61 which is located in the reversing circuit shown in Figures 3 and 5 and which includes the gas filled, grid controlled thyratrons I68 and I10. It will be seen that these tubes have electrical connection of current through the primary windings II, 12

and I3. When the switch I42 is closed the condenser I30 is charged by the independent power source and the negative grid bias applied to the grid of tube I21 is sufficient to hold the tube I21 in a non-conductive state.

The resistance I43 is connected across the conductors I32 and I44, Figures 3 and 7, and the adjustable slider I45 is in circuit with the plate of tube I46, said circuit also including the condenser I41 and the adjustable resistor I48. The adjustment of the resistor I48 controls the "on time period, generally referred to as the weld" period. During conduction of tube I 21 current will flow through resistance I43 and accordingly condenser I41 is charged with the charging rate being controlled by adjustment of with conductors and 8|, which lead respectively to the grid points B and C so that the potential on said points B and C is controlled by the conductivity of tubes I68 and I10. The circuit arrangement for said tubes is such that only one tube is conductive at a time and also said'circuit arrangement effects an automatic switching from one tube to the other to thereby change the potentials on points B and C to render the groups of ignitrons controlled thereby alternately conductive so that the welding device produces a form of alternating current such: as shown in Figure 9 without postheat and in Figure 11. with circuit resistances being connected respectively to the plates of tubes I68 and I10. Said opposite ends of the resistances are also connected to each other through condenser I11. The negative end of resistance I13 is joined by conductor I18 to secondary winding I61 of transformer I58. Conductors I80, I8I and I82 connect with the grids ofthe'tubes.

The operation of the reversing or switching circuit above described can best be understood by assuming that tube I68 is conducting so that current flows from the positive end of resistor I13 .through resistance I15 to tube I68. As a result the condensers I11 are charged to the voltage across I15 with the negative terminal of said condensers having connection with the' plate of tube I68. The pulse of current supplied to secondary winding I61 by the discharge of tube I46 is such as to start conduction of tube I10. minal of condensers I 11 is directly connected through tube I10 to the cathode of tube I68. This automatically stops conduction through tube I68 since its plate is negative, whereas its cathode is now positive. However, tube I10 continues to conduct and the voltage developed across resistance I83 is such as to maintain tube I68 in a nonconductive state until the next pulse of current is delivered to secondary winding I61. The next pulse produces the same action with respect to tube I10. which is rendered nonconductive as IE8 becomes conductive again. The switch from one tube to the other is therefore automatic, being effected by a current pulse delivered to winding I61.

The potential applied to conductor 8I and -thus to grid point C is obtained from the voltage between slider I and the positive end of resistance II9 plus the voltage from slider I45 and the positive end of resistance I43, the sum of these voltages alternating between plus' 90 or minus 110, depending'on whether tube I 21 is conducting or nonconducting. To the above potential must be added the voltage across resistance I15 and which alternates between zero and minus 480 or more, depending on whether tube I68 is not conducting or is conducting. If said tube IE8 is not conducting the voltage on grid point C when the tube I21 fires, which initiates the welding period, will be plus 90. Ac-

cordingly, the thyratrons having connection with grid point C will fire and render ignitrons I1, 2I and 25 conductive to effect a flow of current through the primary windings of the welding transformer.

The potential on point B is the sum of the voltages across the positive end of resistance I I 9, resistance I43 and the voltage across resistance I16. The potential on grid point B will be plus 90 when tube I10 is not conducting and when control tube I21 is conducting. Accordingly. each time tube I21 conducts for a welding period either grid point C and associated thyratrons and ignitrons, or grid point B and associated thyratrons and ignitrons, are rendered conductive, depending on whether tube I68 or I10 is conducting.

In the welding of aluminum alloys a postheating current is employed following the welding pulse to slow down the rate of cooling of the weld metal in order to avoid cracking and fissures due to too rapid cooling. Slow decay is effected by a current decay control including the postheating phase shift circuit which is made operative at the proper time when the various When this takes place the positive terg switches shown in Figure 3 are located in postheat position, that is, No. 2 position. The circuit elements function as follows for postheatmg.

After tube I21 fires for a weld period the welding time is governed by the charging of capacitor I41 through the adjustable resistor I48. Eventually tube I 46 will discharge capacitor I41 at a positive pulse from peaking transformer I50, said tube I46 discharging capacitor I41 only through winding I55 of transformer I51 since winding I55 is not now in circuit therewith by reason of the No. 2 position of switch I53. As a result of the No. 2 position of switches I6I and I62 the secondary winding I64 of said transformer I51 is now located in the grid-cathode circuit of the gas filled, grid controlled tube I84 having a control grid I 05 which is electrically connected to a peaking transformer I86 through the rectifying circuit I81. The plate of said tube I84 is connected to conductor I44 and its cathode has connection through resistor I88 with conductor I32. The circuit including the condenser I90 and the adjustable resistor I9I is in parallel with resistor I88, and it will be understood that the adjustable resistor I 9I controls the postheating period by controlling the charging rate of condenser I90. The pulse delivered to winding I64 when tube I46 discharges is sufiicient to drive the grid I positive and tube I84 is thus rendered conductive to causecurrent to flow through resistance I88 since these elements are in parallel with resistance I43. A conductor I92 connects the positiveend of resistance I88 with the grid controlled vacuum tube I93 shown in Figure 4 and the action of current flow through resistance I88 is such as to change the grid bias on tube I93 from negative to positive so that tube I93 is rendered conductive.

Tube I93 has its independentpower supply consisting of transformer I94, the full wave rectifier I95, and filter circuit consisting of capacitors, reactor and bleeder resistor I96. The negative end of the power supply is joined through conductor I91 to slider I20. Tube I96 is in series with the relay windings 200 and MI and said windings together with tube I93 constitute a parallel connection across resistance I96. When tube I93 is conducting said relays are energized and the contactors in the phase shift circuits are actuated. The normally closed contactors I00 are caused to open and the normally open contactors II4 are caused to close. Whatever may be the setting for the welding phase shift circuit it will be understood that the postheating phase shift circuit has a setting so as to materially delay the firing of the thyratrons and as a result the welding current is considerably reduced to reduce the heating efiect accordingly. Therefore, this controlled decay of the welding current is such as to properly anneal the weld metal to produce a uniformly solid and eflicient weld.

The timing for the postheating period is effected by means of the condenser I and the gas filled, grid controlled tube 202 having a grid 203. The plate of said tube has connection with said condenser, whereas the cathode of said tube has connection through conductors 204 and 205 with winding I56 of transformer I58, it being understood that switches I53 and I54 are still in No. 2 position. As condenser I90 charges the potential across its plates increases exponentially whereas the voltage across the adjustable resistor I9I decreases exponentially. Eventually a positive pulse from the peaking transformer 206 will rend r ridtzfli pos tive fir n ul1e 2 azand dis hars-in c nd s 89 throueh aid tube. ;A pulse; of current accordingly flows through Winding J56 to energize its secondary winding 161 in the reversing control panel. This pulse will shift th? Conductivity of tubes I88 and 110. Simultaneously therewith acurrent pulse is caused to flow through winding 20? of transformer 1208 havinga secondary winding 269. said secondary winding by reason of the No. 2 position of switches [.59 and 160 is located in the grid-cathode circuit of tube I25 and the current pulse is such as to render I25 nonconductive. This 'action .stops flow of current through the control tube I21 and associated elements and thus termiIlatcs-a welding operation which has included awelding period plus a postheating period for the purposes explained.

With the switch M2 in, open position and control tube I21 nonconducting, it will be seen that condenser I30, which has been charged-during the weld period, will now start to discharge through resistor I 34 which accordingly controls the cool time. As condenser 13!) discharges a point is reached when the grid bias on grid 128 of tube 121 will have been rendered sufficiently positive fora pulse from peaking transformer IM to again fire the control tube I21. When tube I2! is rendered conductive current flow takes place through its associated circuit and another 0 weld period is initiated with postheating taking place as long as the various switches are located in their .No. 2 position, Figures 10 and 11 illustrating single and multiple welding operations respectively with controlled decay of the welding the magnitude of the welding current and the I magnitude of the postheating current, and means automatically operative at a predetermined point in the welding operation for rendering one of said phase shift circuits operative and the other inoperative.

2. In a welding system, a welding transformer, an alternating current supply source electrically connected to the input of said transformer, a welding load circuit electrically connected to the output of said transformer, means for producing in the load circuit an impulse of welding current, said current being characterized as of modulated shape consisting of a pulse of welding current followed by a controlled decay of the current for postheating, said means including a normally operative phase shift circuit for controlling the magnitude of the welding current and a normally inoperative phase-shift circuit for controlling the magnitude of the postheating current, and means automatically operative at a predetermined point in the welding operation for rendering the first mentioned phase shift circuit inoperative and the second mentioned phase shift circuit operative.

3. a. welding system, a welding transformer,

an. alternating. -.curr,ent-:sul1 source electrically connected to *the. input of said transformer. is weldin load circuit electrically connected "to :the output of-said transformer, means for producing in-the load circuit-an impulse of welding current, saidcurrent heingcharacterized as of modulatedshape consisting of a pulse of welding current followed by a controlled-decay of the ourrent for :postheatine. said means including a normally operative phase shift circuit for con-- trolling the magnitude of the welding current and a normally inoperative phase shiftmircuit forcontrolling the magnitude of the postheating current, means for timing the duration of the Welding ipcri'od, other means for timing the duration of -the-posthcating period, and-electronic circuit means connecting the timing means with the other timing means and rendered effective y said timing means at the end of the welding period for rendering the other timing :means operative for timing the postheating period and for also simultaneously effecting a switch in the phase shift circuits, whereby the normally-operative phase "shift circuit rendered inoperative and the normally inoperative phase shift circuit is rendered operative.

4. In a welding system, a welding transformer. an alternating current supply source electrically connected to the input of said transformer, a welding load circuit electrically connectedto the output of said transformer, means for producing in the load circuit an impulse of welding current, said current being characterized as of mod-- ulated shape consisting of a pulse .of welding current followed by a controlled decay- .of the current. for postheating, said means including s normally operative phase shift circuit for controlling thev magnitude of the welding current and a normally inoperative. phase shift circmt for controlling the magnitude of the postheating current,;ad.iustable means including electronic circuit elements for timing the duration of the welding period, other adjustable means including other electronic circuit elements for timing the duration of the postheating period, and electronic circuit means rendered effective by said first mentioned timing means by its action in terminating the welding period for starting :operation of the other timing means for timing the postheating period and for effecting a switch in the phase shift circuits, whereby the normally operative phase shift circuit is rendered inoperative and the normally inoperative, phase shift circuit is rendered operative.

'5. In a welding system of the three phasethree winding type wherein three windings are connected in delta relation to a three phase supply and wherein a loadv circuit is inductively associated with said windings, of a phase shift circuit including adjustable means for selecting a particular value of current for the load circuit and thus a particular welding heat, timing means for the welding period, a second phase shift circuit also including adjustable means for selecting a lower value of current for the load circuit for postheating the weld metal, means for timing the postheating period, and electronic circuit means rendered effective by the timing means for timing the welding period for rendering the first mentioned. phase shift circuit inoperative and the second mentioned phase shift circuit operative and for simultaneously starting operation of the timing means for timing the postheating period.

6. In a welding system, in combination, a

source of pclyphase alternating current, an inductive device having primary windings corresponding in number to the phases of the alternating current source, circuit means connecting each winding to its respective phase of said source, at least one electric discharge valve for each wind ing for controlling flow of unidirectional currents through the winding, means controlling the firing of the electric discharge valves including a normally operative phase shift circuit and a normally inoperative phase shift circuit, whereby the value of the welding current is determined by the setting of that phase shift circuit which is operative at the time, and means adapted to operate at a predetermined point in the welding operation for rendering the normally operative phase shift circuit inoperative and the normally inoperative phase shift circuit operative.

'7. In a welding system, in combination, a source of polyphase alternating current, an inductive device having primary windings corresponding in number to the phases of the alternating current source, circuit means connecting each winding to its respective phase of said source, at least one electric discharge valve for each winding for controlling flow of unidirectional currents through the winding, means controlling the firing of the electric discharge valves for producing a welding current including an adjustable phase shift circuit that isnormally operative, timing means for timing the duration of the welding current, other means controlling the firing of the electric discharge valves for effecting a decay in the welding current in a controlled manner for postheating purposes including an adjustable phase shift circuit and which is normally inoperative, second timing means for controlling the duration of the postheating period, and means rendered operative by the action of the timing means in timing the duration of the welding current for effecting a switch in the phase shift circuits, whereby the first mentioned phase shift circuit is rendered inoperative and the second mentioned phase shift circuit is rendered operative, said means also simultaneously starting operation of the second timing means for timing the duration of the postheating current.

8. In a welding system of the three phase-three winding type wherein three windings are connected in delta relation to a three phase supply, and wherein a load circuit is inductively associated with said windings, a pair of inversely connected discharge valves for each winding in series with their winding, a firing valve for each discharge valve for rendering the discharge valve conductive when the firing valve is conductive, said discharge valves comprising two groups with each group having one valve in each winding so that when one group is conductive current will flow in one direction through the windings and in an opposite direction when the other group is conductive, means for producing in the load circuit an impulse of welding current of modulated shape consisting of a pulse of welding current followed by a controlled decay of the current for postheating, said means including a normally operative phase shift circuit for controlling the magnitude of the welding current and a normally inoperative phase shift circuit for controlling the magnitude of the postheating current, said phase shift circuits controlling the welding and postheating currents by phase shifting the voltage applied to the grids of the firing valves with respect to the line voltage of their respective phase,

means adapted to operate at a predetermined point in the welding operation for rendering the first mentioned phase shift circuit inoperative and the second mentioned phase shift circuit operative, and other means including a reversing circuit adapted to be energized at the end of the welding operation for alternating the conductivity of the two group of discharge valves.

9. In a welding system of the three-phase winding type wherein three windings are connected in delta relation to a three phase supply, a pair of inversely connected discharge valves for each winding in series with their winding, a firing valve for each discharge valve for rendering the discharge valve conductive when the firing valve is conductive, said discharge valves comprising two groups with each group having one valve in each winding so that when one group is conductive current will flow in one direction through the windings and in an opposite direction when the other group is conductive, means controlling the conductivity of the firing valves including a normally operative phase shift circuit and a normally inoperative phase shift circuit, whereby the value of the welding current is determined by the setting of that phase shift circuit which i operative at the time, said phase shift circuits controlling the value of the welding current by phase shifting the voltage applied to the grids of the firing valves with respect to the line voltage of their respective phase, means adapted to operate at a predetermined point inthe welding operation for rendering the first mentioned phase shift circuit inoperative and the second mentioned phase shift circuit operative, and other means including a reversing circuit adapted to be energized at the end of the welding operation for alternating the conductivity of the two groups of discharge valves.

10. In a welding system, a source of polyphase alternating current, a welding transformer having primary windings each having asymmetrically conductive electric discharge valves in circuit for controlling flow of unidirectional current impulses through the windings, a phase shift circuit for selecting the value of the current caused to flow through the primary windings to thereby produce a welding current of selected magnitude and thus a particular welding heat, a second phase shift circuit for selecting a current of lower value for flow through the primary windings to produce a postheating current, switch structure having two positions of adjustment, said switch structure determining the character of the welding operation according to the setting of the switch structure, said switch structure in one position rendering the first mentioned phase shift circuit effective for producing welding operations each consisting of a pulse of welding current only, and said switch structure in another position rendering both phase shift circuits effective in sequence for producing welding operations each consisting of a pulse of welding current followed by a postheating current.

11. A welding system as defined by claim 10, additionally including timing means for timing the duration of the pulse of welding current, other timing means for timing the duration of the postheating period, said switch structure in said one position rendering only the first mentioned timing means effective and said switch structure in its other position rendering both timing means effective in sequence.

12. In a welding system, a source of polyphase alternating current, a welding transformer having primary windings each having asymmetrically conducting electric discharge valves in circuit for controlling flow of unidirectional current impulses through the windings, a welding phase shift circuit for controlling the value of current caused to now through the primary windings to thereby produce a welding current of predetermined magnitude, a postheating phase shift circuit for controllin the value of the current caused to flow through the primary windings to thereby produce a postheating current of lower value than the welding current, normally closed cont-actors for the welding phase shift circuit rendering the same normally operative, normally open contactor for the postheating phase shift circuit normally rendering the same inoperative, relay means for actuating the contactors when energized to cause the normally closed contactors to open and the normally open contactors to close whereby the welding phase shift circuit is rendered inoperative and the postheating phase shift circuit is rendered operative, and means adapted to operate at a predetermined point in the welding operation for energizing said relay means.

13. A welding system as defined by claim 12 additionally including timing means for timing the duration of the welding current, other timing means for timing the duration of the postheating current, and electronic circuit means rendered effective by said first mentioned timing means at the end of the welding current period for energizing the relay means to effect a switch in the phase shift circuits and for simultaneously starting operation of said other timing means for timing the postheating period. 14. In a welding system, a source of polyphase alternating current, a welding transformer having primary windings, two groups of asymmetrically conductive electric discharge valves in circuit with said windings and adapted to be alternately conductive for controlling flow of unidirectional current impulses through the windings, first in one direction and then in the opposite direction, a welding phase shift circuit for controlling the firing of the discharge valves to produce a welding current of predetermined magnitude, a postheating phase shift circuit for also controlling the firing of the discharge valves to produce a postheating current of lower value than the welding current, timing means for timing the duration of the welding current, timing means for timing the duration of the postheating current, switch structure for determining the character of the welding operation according to the setting of the switch structure, said switch structure in one position rendering only the welding phase shift circuit and said first mentioned timing means effective to thereby produce welding operations each consisting of a welding current only, said switch structure in another position rendering both phase shift cir cuits effective in sequence and both timing means also effective in sequence for producing welding operations each consisting of a welding current followed by a postheating current, and a re- 18 versing circuit adapted to be energized at the end of each welding operation for alternating the conductivity of the two groups of discharge valves.

15. In a welding system, a source of polyphase current, a welding transformer having primary windings corresponding in number to the phases of said source and having a load circuit inductively associated with the primary windings, circuit means electrically connecting each primary winding to its respective phase of said source, a pair of inversely connected discharge valves for each winding in series with their winding, a firing valve for each discharge valve for rendering the discharge valve conductive when the firing valve is conductive, circuit means for controlling the conductivity of said firing valves and thus the discharge valves in a manner to produce a welding current of predetermined magnitude with controlled decay of the current for postheating, said circuit means including a normally operative phase shift circuit for controlling the magnitude of the welding current, and a normally inoperative phase shift circuit for controlling the magnitude of the postheating current, welding current timing means for timing the duration of the welding current, postheating current timing means for timing the duration of the postheating current, circuit means electrically connecting the welding current timing means with the postheating current timing means, and electronic means in the circuit means rendered operative by the action of the welding current timing means in timing the welding current for initiating operation of the postheating current timing means and for simultaneously effecting a shift in the phase shift circuits, whereby the welding current phase shift circuit becomes inoperative and the postheating current phase shift circuit becomes operative.

16. A welding system as defined by claim 15, wherein certain discharge valves comprise one group for passing current through the windings in one direction when conductive and the remaining discharge valves comprise a second group for passing current through the windings in an opposite direction when conductive, and additionally including a reversing circuit adapted to be energized by the action of the postheating current timing means in terminating a welding operation for alternating the conductivity of the two groups of discharge valves.

JULIUS L. SOLOMON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,200,077 Dawson May 7, 1940 2,251,237 Biven July 29, 1941 2,306,229 Somerville Dec. 22, 1942 2,306,230 Somerville Dec. 22, 1942 2,374,044 Smith Apr. 17, 1945 

